function output_indexes= select_specie(obj,varargin)
%Select atoms of a given element

natoms = obj.natoms;
indexes = obj.Atoms.keys;
k2 = 0;
output_indexes = [];
for k=1:natoms
    
    if (obj.Atoms(indexes{k}).Kind == char(varargin{1}))
       k2 = k2 + 1;
       output_indexes(k2) = indexes{k}; 
    end
    
end


end